The subject invention relates to a parking brake system for a vehicle including a pneumatically controlled brake actuator that mechanically locks a service brake in a parked condition. The parking brake system can be used in a vehicle having an electronic braking system or can be used in a vehicle that does not have an electronic braking system.
Traditionally, heavy commercial vehicles utilize spring actuators to provide the energy needed for a parking brake function. These heavy commercial vehicles often include electronic braking systems that provide the primary braking function. The primary brake function is a main or foundation brake function that is used to stop or slow rotation of a vehicle wheel during vehicle operation. The parking brake function is usually a separate system that is used to lock a vehicle wheel in a brakes applied position when the vehicle is parked. Traditionally, spring actuators are used for providing the parking and service brake functions. This increases cost and reduces available packaging space for other wheel components.
It is possible for the electronic braking system (EBS) to include an electronic parking control with a hand operated lever or handle that is moved by an operator into a park position. In response to movement of the hand operated lever into the park position, an electronic park signal is generated to control actuation of the brakes for parking. The electronic parking control uses the EBS to apply and release the brakes for parking. In such a system, the service actuators are used for parking and when the desired level of braking is achieved, the brakes are mechanically latched in the applied state. Not all vehicles are equipped with an electronic braking system (EBS). Further, some vehicles have an EBS but do not want the parking brake system to be electronically controlled. Also, it is desirable to eliminate the need for separate park spring actuators. Thus, there is a need for a parking brake system that pneumatically controls parking by using a service brake actuator, and which can be used in a vehicle with EBS or without EBS.